The present invention relates to a compound semiconductor constituted using a AlGaInP-based semiconductor material, a method for manufacturing the same, a semiconductor device, and a method for manufacturing the same.
A digital versatile disk (DVD) apparatus, which can record information with quite a high density, is rapidly spreading in fields of personal computers and audio-video apparatuses. Recently, a DVD apparatus that can write or re-write information in a DVD is in particular expected to further spread as a next-generation video recorder (DVD recorder) to replace, for example, a mass-storage external memory (e.g., a DVD-R or a DVD-RAM) or a videotape recorder. To this end, it is an important challenge to improve a write rate.
In the DVD apparatus that can write or rewrite data to the DVD, a semiconductor laser device that outputs a red light at a wavelength of about 650 nm is employed as a pickup light source for reading or rewriting data. To improve the write rate of the DVD apparatus, therefore, it is necessary to ensure high power output of the semiconductor laser device.
A conventional semiconductor laser device capable of outputting a red light will now be described with reference to the drawings.
FIG. 9 is a block diagram of a sectional configuration of the conventional semiconductor laser device. As shown in FIG. 9, an n-type cladding layer 61 consisting of AlGaInP, an active layer 62 having a quantum well structure in which an AlGaInP layer and a GaInP layer are alternately provided, a first p-type cladding layer 63 consisting of AlGaInP, and an etching stop layer 64 consisting of GaInP are layered on a principal surface of a substrate 60 consisting of n-type GaAs in this order. A second p-type cladding layer 65 consisting of AlGaInP and processed into a ridge shape is formed on the etching stop layer 64. A first contact layer 66 consisting of p-type GaInP is formed on the second p-type cladding layer 65. A first current block layer 67 consisting of n-type AlInP and a second current block layer 68 consisting of n-type GaAs are formed on the etching stop layer 64 so as to bury side regions of the second p-type cladding layer 65 and the first contact layer 66. Further, a second contact layer 69 consisting of p-type GaAs is formed on the first contact layer 66 and the second current block layer 68. The respective semiconductor layers 61 to 69 on the substrate 60 are formed by crystal growth using a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxial (MBE) method.
An ohmic n-side electrode 70 is formed on a surface of the substrate 60 opposite to the surface on which the n-type cladding layer 61 is formed, and an ohmic p-side electrode 71 is also formed on the second contact layer 69.
As p-type dopant for AlGaInP, zinc (Zn) is normally used. However, zinc is high in diffusion coefficient relative to an AlGaInP-based semiconductor material. Due to this, at a crystal growth step or a heat treatment step when manufacturing, for example, a semiconductor laser device, zinc is diffused from the first p-type cladding layer 63 toward a quantum well of the active layer 62. If so, the zinc diffused into the quantum well of the active layer 62 generates a non-radiative recombination center in the active layer 62, thereby resulting in a deterioration in an emission efficiency of the semiconductor laser device. In addition, if the zinc serving as the dopant is diffused into the active layer 62, a crystallinity of the quantum well is degraded, thereby resulting in a deterioration in a reliability of the semiconductor laser device.
Magnesium (Mg) is, by contrast, known as a dopant that exhibits a p-type conductive property in AlGaIn and that is low in diffusion coefficient. However, magnesium strongly adheres to piping and a reaction chamber of a crystal growth apparatus. Due to this, it is known that, after supply of a material is stopped or at the next crystal growth step, unintended magnesium doping occurs, that is, magnesium produces a so-called memory effect.
FIG. 10 shows a result of an experiment conducted by the inventors of the present invention to confirm the memory effect produced by magnesium. In the experiment, when a semiconductor layer consisting of GaAs is grown on a substrate consisting of GaAs by the MOCVD method, four Mg doped-region (region that supplies an Mg raw material) layers A are formed at predetermined intervals during growth of the semiconductor layer. A magnesium concentration profile of the semiconductor layer in which the four Mg doped-region layers are formed is measured by a secondary ion mass spectrometry (SIMS). As can be seen from FIG. 10, even if the supply of the magnesium raw material is stopped during the growth of the GaAs semiconductor layer, the magnesium exhibits a concentration of at least a second half level of 1016.
To avoid this memory effect, a method in which a reaction chamber for growing a semiconductor layer into which a p-type dopant, for example, is not doped and the other reaction chamber for doping the p-type dopant are separately used is disclosed in Japanese Patent Application Laid-Open No. 11-112030.
The method disclosed therein, however, has a disadvantage of complicated manufacturing facility and manufacturing steps such as a need to prepare a plurality of reaction chambers and a need to move a sample (substrate) among the plural reaction chambers.
Furthermore, the conventional method has the following disadvantages. When the substrate is moved among the plural reaction chambers, it is necessary to interrupt and resume the crystal growth. Due to this, as compared with continuous formation of a multilayer structure, a flatness of an interface between the respective semiconductor layers and a steepness of a composition change on the interface are deteriorated.